If you post around and get in on conversations, people will become your friends
If you want to visit other people's towns or have them visit yours you can make a thread in the Train Station. That's an easy way to make friends! Before you do any sort of online interaction from the Bell Tree, be sure to check out this: http://www.belltreeforums.com/showthread.php?76645-Guidelines-for-Animal-Crossing-Online